News Release Number: STScI-2005-26

Hubble Finds Mysterious Disk of Blue Stars Around Black Hole

September 20, 2005: Astronomers using NASA's Hubble Space Telescope have identified
the source of a mysterious blue light surrounding a supermassive
black hole in our neighboring Andromeda Galaxy (M31). Though the
light has puzzled astronomers for more than a decade, the new
discovery makes the story even more mysterious. The blue light is
coming from a disk of hot, young stars that are whipping around
the black hole in much the same way as planets in our solar system
are revolving around the Sun. Astronomers are perplexed about how
the pancake-shaped disk of stars could form so close to a giant
black hole. Andromeda and its complex core can be seen in the
illustration and two images [above]. The illustration [lower, right]
shows the disk of blue stars nested inside a larger ring of red
stars. The Hubble photo [upper, right] reveals Andromeda’s bright
core. The image at left shows the entire galaxy.

Q & A: Understanding the Discovery

1.
How could the disk of blue stars have formed around the black hole?

Astronomers do not know how the blue stars could have formed
around the black hole. The stars are massive and have short life
spans, so astronomers do not think they coincidentally witnessed
a once-in-a-lifetime event. They think the mechanism that created
the disk of stars probably formed other disks in the past and will
trigger the formation of similar disks in the future.

2.
Will the stars fall into the black hole?

The stars will not fall into the black hole because they are
in orbit around it, just as our Earth will not plummet into
our Sun because it revolves around our star. The black
hole's intense gravitational grip means that the stars must
orbit very fast.

3.
Do other galaxies have blue stars in their cores?

Astronomers have seen blue light in the cores of other
spiral galaxies. Even our Milky Way Galaxy has a cluster of
blue stars at its core. Finding blue stars in the cores of
two neighboring galaxies, Andromeda and the Milky Way,
suggests that other galaxies may have them.